A gas turbine is a turbomachine in which a gas under pressure expands. It includes a turbine or expander, a compressor connected upstream thereof, and a combustor connected between the two. All of the blades of the compressor and of the turbine are referred to collectively as the blading. In that context, a distinction is drawn between rotor blades and guide blades. A ring of rotor blades, together with the associated ring of guide blades, is referred to as a stage. It is common for the blading of the turbine or of the compressor to be multistage.
The guide blades are fixedly integrated into the casing of the compressor or of the turbine and guide the working medium (intake air or hot gas) at the optimum angle onto the rotor blades, which are on rotating shafts. The coupling of the mechanically useful power, between the machine and the fluid, occurs via the rotor blades.
The working principle is based in this context on the cyclic process (Joule process): this compresses air by means of the blading of one or more compressor stages, then mixes this air with a gaseous or liquid fuel in the combustor and ignites and combusts the mixture. In addition, the air is used for cooling, in particular of components subjected to high thermal stresses. This produces a hot gas (a mixture of combustion gas and air) which expands in the subsequent turbine part, wherein thermal energy is converted to mechanical energy and then drives the compressor. In a shaft engine, the remaining portion is used to drive a generator, a propeller or other rotating loads. In a jet engine, by contrast, the thermal energy accelerates the hot gas stream, producing thrust.
The hot gas subjects components of gas turbines to high thermal stresses. An increase in operating temperatures is also desirable as it allows improvements in efficiency to be achieved. In order that the material temperatures do not exceed the strength limits, a supply of coolant, for example air, is therefore provided. On the way to the provided point of action of the coolant, the latter is however already heated by the high temperatures. This heating can, in certain circumstances, be so great that the provided cooling effect of the coolant at the point of action is too small. This increases the thermal load and thus reduces the service life of the component at the point of action. In this case, the coolant is therefore frequently conveyed in separate coolant bridging lines.